Declining and fluctuating prevalence values of hearing impairment in 18-year old Swedish men during three decades

Explaining better hearing in Norway: a comparison of two cohorts 20 years apart - the HUNT study

Background

The hearing function at a given age seems to have improved in more recent born cohorts in industrialized countries. But the reasons for the improvement have not yet been explained.

Methods

We investigated the extent to which better hearing in Norway is attributed to modifiable risk factors by using representative demographic and audiometric data from two cohorts of the Trøndelag Health Study, HUNT2 (1996–1998) and HUNT4 (2017–2019). We estimated natural indirect effects using causal inference methods in order to assess whether cohort improvement in hearing thresholds (HTs) was mediated by occupational noise exposure, recurrent ear infections, smoking and education.

Results

The improvement in HTs from HUNT2 to HUNT4 was 2.8 and 3.0 dB at low respectively high frequencies. Together all risk factors mediated this improvement by 0.8 dB (95% CI 0.7–0.9) and 0.8 dB (95% CI 0.7–0.9) respectively, corresponding to mediated proportions of 27 and 28%. Substantial mediation was specifically found for occupational noise in men and recurrent ear infections in women (mediated proportions of 11 and 17% at high frequencies, respectively).

Conclusions

Increased education, less occupational noise exposure, ear infections and smoking contributed considerably to better hearing in Norway the last two decades.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-10301-1.

Better Hearing in Norway: A Comparison of Two HUNT Cohorts 20 Years Apart

OBJECTIVE

To obtain updated robust data on a age-specific prevalence of hearing loss in Norway and determine whether more recent birth cohorts have better hearing compared with earlier birth cohorts.

DESIGN

Cross-sectional analyzes of Norwegian representative demographic and audiometric data from the Nord-Trøndelag Health Study (HUNT)-HUNT2 Hearing (1996-1998) and HUNT4 Hearing (2017-2019), with the following distribution: HUNT2 Hearing (N=50,277, 53% women, aged 20 to 101 years, mean = 50.1, standard deviation = 16.9); HUNT4 Hearing (N=28,339, 56% women, aged 19 to 100 years, mean = 53.2, standard deviation = 16.9). Pure-tone hearing thresholds were estimated using linear and quantile regressions with age and cohort as explanatory variables. Prevalences were estimated using logistic regression models for different severities of hearing loss averaged over 0.5, 1, 2, and 4 kHz in the better ear (BE PTA4). We also estimated prevalences at the population-level of Norway in 1997 and 2018.

RESULTS

Disabling hearing loss (BE PTA4 ≥ 35 dB) was less prevalent in the more recent born cohort at all ages in both men and women (p < 0.0001), with the largest absolute decrease at age 75 in men and at age 85 in women. The age- and sex-adjusted prevalence of disabling hearing loss was 7.7% (95% confidence interval [CI] 7.5 to 7.9) and 5.3% (95% CI 5.0 to 5.5) in HUNT2 and HUNT4, respectively. Hearing thresholds were better in the more recent born cohorts at all frequencies for both men and women (p < 0.0001), with the largest improvement at high frequencies in more recent born 60- to 70-year old men (10 to 11 dB at 3 to 4 kHz), and at low frequencies among the oldest.

CONCLUSIONS

The age- and sex-specific prevalence of hearing impairment has decreased in Norway from 1996-1998 to 2017-2019.